Mercury oxide-containing optical glasses

ABSTRACT

The invention relates to a series of new glasses of the low crown and low flint type but with refractive indices lower than those previously obtainable. The crux of the invention provides for the controlled inclusion of an effective amount of mercury oxide in glass compositions.

United States Patent [721 Inventors Milton E. Winyall, Ellicott City,2.345.311 3/1944 Wilson 106/306 XR Thomas E. McGoury, Severna Park,2,435,600 2/ 1 948 Rafton. 106/306 both of Md., and Julian H. Chaudet,2,540,182 2/ 1951 Albert 106/308 B Fairfax, Va. 2.671.032 3/1954Thompson 106/306 [21 Appl. Nov 816,033 3.494.731 2/1970 Reynolds et a1106/306 XR P t d t. 26, 1971 [45] e 0c 745.068 10/1966 Canada 106/306[73 I Assignee W. R. Grace & Co., New York, NY.

[541 DRY REDISPERSIBLE SATIN WHITE AND METHOD OF PREPARING 8 Claims, NoDrawings 152] U.S.Cl....... 106/306, 106/308 B. 308 N. 308 Q [51 Int. ClC09c 1/02 150] Field of Search 106/306. 309. 308 B. 308 Q: 23/122References Cited UNITED STATES PATENTS 3.494,731 2/1970 Reynolds 106/308B Primary Examiner-James E. Poer Assistant Examiner- H. M. S. SneedAttorneys- Lawrence S. Squ1res and Kenneth E. Prince ABSTRACT: Dryingmethods of producing a dried form of satin white which is easilyredispersible in 11quid carriers. are disclosed. In one aspect themethods are characterized by spray drying under specific temperatureconditions. Satin white has utility as a pigment for both paints andpaper coatings.

DRY REDISPERSIBLE SATIN WHITE AND METHOD OF PREPARING BACKGROUND OF THEINVENTION 1. Field of the Invention This invention relates to methods ofdrying satin white. A further aspect of this invention relates tomethods of forming a dried satin white product which is easily dispersedin liquid carriers.

2. The Prior Art Satin white is a chemical compound having theapproximate chemical formula: 3CaO'Al2O 3CaSO4- 3l-32 H2O. which findsextensive commercial use as a pigment. particularly in paints. paper andpaperboard coatings. Because of its bright white color and because itgenerally possesses good coating properties. e.g. gloss. brightness.opacity. smoothness and ink receptivity. it is extensively used as apaper coating pigment Satin white is typically prepared by reactingaqueous solutions of alum with aqueous dispersions of quick lime orslaked lime in amounts stoichiometrically equivalent to their ratio inthe satin white composition. It has also been found that by varying thereaction conditions. the size and shape of the satin white particlesformed can be varied and consequently also its gloss, smoothness.whiteness and hiding power. which are largely a function of particlesize and shape.

Satin white is typically prepared. and used, in the form of an aqueousslurry having a satin white solids content of from to 35% and preferablyfrom to by weight. One of the problems incident to satin white. is thatit cannot be satisfactorily redispersed after it has been dried. Thusthe satin white pigment must be either prepared at the job site. e.g.paper mill. or must be shipped in the form of an aqueous slurry having asatin white solids content of 20 to by wt. This necessarily increasesthe shipping costs due to the large amount of water which must beshipped with the satin white. Thus it would be very desirable to developa method of drying satin white in a form which is readily liquiddisperable and thus avoid the excessive shipping costs or the necessityfor preparing the satin white at the job site. The prior art has alsorecognized this problem and has attempted to develop methods, ofalleviating this dispersion problem, such. as for example, thatdescribed in US. Patent 2,671,032; which requires intimately mixing aprotein material with satin white followed by the addition of a hydratedalkali metal phosphate. This method necessarily increases the cost ofthe ultimate product and does not represent a complete solution to theproblem.

OBJECTS AND SUMMARY Objects It is therefore an object of the inventionto provide improved methods and means for drying satin white and toprovide an improved dried satin white product. It is afurther object ofthe invention to provide methods and means for (1) providing a satinwhite slurry. preferably an aqueous slurry, having a solids content ofabout from 5 to [1% by wt.

(2) adding a suitable dispersant to the satin white slurry in a quantityequal to about from .6 to 2.5% by wt. based on the weight of solid satinwhite in the slurry.

(3) spray drying the diluted slurry containing the dispersant in a spraydrier using. countercurrent flow. a heating gas inlet temperature in therange of about from 650 F. to 750 F. and controlling the flow rate ofthe heating gas. relative to the rate of the diluted slurry being fedinto the spray drier. such that the heating gas has an outlet or exittemperature in the range of about from 250 to 350 F. We have foundparticularly good results to be obtained using air as the heating gas.

Typically the slurry will be at ambient temperatures. when it is fedinto the spray drier though other temperatures can be used. Thecharacteristics of spray driers are such that by supplying the heatinggas to the spray drier at a specific temperature (or temperature range)and then controlling the outlet temperature of the heating gas byadjusting the flow rate of the heating gas. the satin white is subjectedto. within narrow limits. at particular drying temperature-time profile.which results in the production of a dried product which is easilydispersible in liquid mediums. such. as for example. water. We have alsofound that if the temperature limits are not maintained the resultingsatin white product will notsatisfactorily disperse in liquid carriermediums, typically water. and/or will not be satisfactorily dried. Incontrast to this. the dried satin white product of our invention.disperses readily in liquid carriers. and typically has a particle sizein the range of about from 0.1 to 0.3 microns wide. and about froml.03.0 microns long. By readily dispersible in liquid mediums we meanthat when the dried satin white product of our invention is added towater containing from about 1.75% to 2.5% dispersant. based on theweight of the satin white. and mixed in a Waring Blender. as much as 25%satin white. based on total weight of mixture. can be brought into astable disper sion suitable for subsequent formulation into a papercoating An unsatisfactory dispersion will be shown by this type topossess a large number of agglomerates.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTSConsidering now our invention in greater detail a slurry of satin whitehaving a satin white solids content ob about from 5 to l 1% by wt. isprepared. Typically this slurry is prepared by merely diluting acommercial satin white slurry or the satin 5 white slurry reactionproduct obtained from a typical process used for preparing satin white.to the desired 5 to l 1% solids content. Typically. the satin white isprepared and is commercially available in the form ofa slurry having asolids content of about from 20 to 35% by wt. Also the liquid carrierspray drying satin white and to provide a dried form of 0 medium usuallywill be water though other suitable carrier satin white which is readilydispersible.

It is a still further object of the invention to provide methods andmeans for spray drying satin white and to provide a form of dry satinwhite which is readily dispersible in a liquid medium. such as forexample water. and which has a particle size and shape particularlydesirable for use in paper coatings.

Additional objects will be apparent. and in part obvious. from thefollowing description and the appended claims.

vention the process of which. in summary. comprises the steps of:

could be used. The actual preparation of the satin white compound itselfis well known to the art and does not form part of our invention;suitable methods for preparing satin white can. for example. be obtainedfrom US. Patent Nos. 2.310.693: and 3,391,995. We have further foundthat best spray drying results are obtained by using slurry solidscontents of about from 5 to 6% by wt.

' The next step of our process comprises admixing the dilute satin whiteslurry with about from .6 to 2.5% by wt. (based on the weight of thesolid satin white in the slurry) of a sodium hexametaphosphate typedispersant. which has a Na O to P ratio of 1.121 and contains at least65% by wt. P 0 sold under the trademark Calgon; especially when used ata concentration of about .6 to 1% by wt. (based on the wt. of satinwhite).

In the next step of our process, the diluted satin white slurrycontaining the admixed dispersant is spray dried under carefullycontrolled temperature conditions. Preferably the dispersant isthoroughly mixed with the satin white slurry prior to spray drying.

In the operation of a typical spray drier, a slurry of the material tobe dried. is sprayed into a chamber into which a heating gas is flowing.The flow of heating gas can be either countercurrent or cocurrent to thedirection of flow of the slurry spray. The liquid portion of the slurryis rapidly evaporated from the slurry, leaving the dried product whichis then collected. The details of the operation of spray driers are wellknown to the art. and further information as to these details can, forexample, be obtained from the following US. Patent Nos. 3.049.174; and3,110,444. As noted above, the spray drier can be operated with eithercocurrent or countercurrent flow of the heating gas and slurry. howeverwe have found best results to be achieved. in our process, usingcountercurrent flow. Therefore the temperatures range which hereinfollow will be for countercurrent flow and suitable adjustments will berequired for cocurrent flow to give effectively the same temperatureprofile effect. This can be obtained by routine energy balancecalculations and optimization tests, well within the scope of anartisan. It is critical to our invention that the heating gas besupplied at an inlet temperature of about from 650 F. to 750 F. and thatthe rate of the heating gas flow be adjusted such, relative to the flowof the slurry. that the outlet or exit temperature of the heating gas isin the range of about from 250 to 350 F. We have found that best resultsare obtained when the heating gas is supplied to the spray drier at aninlet temperature of about 700 F and the flow rate of the heating gasadjusted such. that the outlet gas has a temperature of about 300 F.Typically, and conveniently. the heating gas will be air. though othergases can be used. provided they do not react with the satin white ordispersant. or are not otherwise deleterious to the satin white product.The above heating gas temperatures have been based on air. thus whereother gases are used having different heat capacities a modification inthe temperature differentials between the inlet temperature and exittemperature will be required to account for this difference. The driedsatin white product will typically have an ultimate temperature around105 C.. which is the temperature at which satin white begins to lose itswater of hydration. The important factor being that the spray driedproduct retains a portion of its water of hydration or crystallization.

Because of the nature of spray drying operation and of the hydratedsatin white. the specification of the inlet and outlet temperature ofthe heating fluid is completely definitive of the critical timetemperature relationship or profile to which the satin white issubjected during drying. It is theorized' that this time temperatureprofile is such that the satin white is sufficiently dried to become adry powder and yet still retains a substantial portion of its water ofcrystallization and that liquid dispersibility of the dried product isat least partially attributable to this substantial retention of thewater of crystallization. Best results are obtained when about 25% ofthe water of crystallization is retained. The spray dried product has aparticle size in the range of about from 0.1 to 0.3 microns wide andabout from 1.0 to 3.0 microns long, which is especially desirable forusein paper coatings.

After the satin white has been spray dried it can be shipped to the joblocation in the dry form and then redispersed at the job site. Theredispersion is accomplished by simply mixing the satin white with thedesired quantity of the desired liquid medium carrier, usually water.Best results are obtained when the dried satin white is mixed with asmall amount ofdispersant typically about .52% based upon the wt. ofsatin white.

though this is unnecessary where sufficient dispersant has been addedprior to spray drying. Suitable dispersants have been previouslydescribed. A typical dispersion. used in a paper coating preparationwill have a solids content of about from 20-30% by wt.

A further understanding of the invention can be had from the followingillustrative, but non-limiting. examples.

Example 1 This example illustrates a method of preparing satin white. 1nthis example satin white was prepared as follows: a 560 g. portion ofquicklime (98% CaO) was slaked in 1500 g. boiling water in ajacketedmixer (Model 100T Hobart Mixer). After cooling to 20 C. by circulationof cold water in the jacket. there was added a solution of 990 g.aluminum sulfate [Al (SO4l.-;- l8 H O] dissolved in 3225 g. water. Thissolution was added with stirring over a period of 42 minutes. duringwhich time the reaction mixture reached a maximum temperature of 30 C.

At the end of the reaction the mixture had a pH of 1 1.4 and a solidscontent of 34.2%. Chemical analysis of the vacuum dried product showed:

Mole Ratio Example 2 This example illustrates a method. according to ourinvention. of preparing a spray dried liquid dispersible satin whiteproduct. In this example an aqueous slurry having a satin white solidscontent of35% by wt. was diluted with sufficient water to form a slurryhaving a solids content of about 5% by wt. The slurry was then passed toa conical type spray drier (designated and sold by Boeing Engineering.lnc., of North Brook. New Jersey. as Model BE-499-(onical LaboratoryType) at the rate of 5 gal. per min. Heated air was supplied to thespray drier. using countercurrent flow, at an inlet temperature of 700F. The flow rate of the heated air was adjusted such that the outlettemperature of the air was maintained at 300 F. The resulting productwas a fine white powder. This powder is mixed with 1.75% (based on thewt. of satin white) of sodium polyacrylate and is mixed with water toprepare a dispersion having a 25% by wt. solids content. The dispersionis found to be very satisfactory and suitable for use in formulatingpaper coating.

Example 3 This example illustrates a method. according to our inventionof preparing a spray dried liquid dispersible satin white product. Inthis example a commercial satin white slurry. sold by Hercules PowderCo. under the trademark Hercules Super Satin White Paste, having a 25%by wt. solids content in a water carrier. was diluted with water to a 5%by wt. solids content and then mixed with 1% by wt. (based on the weightof dried satin white) ofa dispersant sold under the trademark Calgon.The slurry was then spray dried in the same manner as in Example 2. Theresulting product is again a white powder which was easily dispersiblein water under the same conditions as in Example 2.

Example 4 in this example the dried satin white products of Examples 2and 3 were dispersed in water and were respectively compounded withidentical quantities of the same paper coating ingredients. into threepaper pigment coatings. The ultimate pigment coatings had the followingcomposition, in terms of parts by weight. 100 parts satin white. 40parts starch. 2.5 dispersant (sodium salt of polyacrylic acid) and 300parts of water. The coatings were then applied to identical papersamples at a coating level of 3300 ft. and the resulting coated papertested for gloss, brightness, opacity, smoothness and ink receptivityaccording to the following TAPPl Tests:

Test Method Brightness TAPPl T452 M-58 Opacity TAPPI T425 m-60 GlossTAPPI T480 ts-65 smoothness TAPPI T490 sm-58 TAPPI Routine ControlMethod No. 19

Ink Receptivity Identical paper pigment coatings were made, but usingthe initial forms of the satin white pastes prior to spray drving. Thesecoatings were then applied to samples of papers identical to those usedfor the spray dried pigment coating, and the same manner as the spraydried pigment coatings. These papers were then tested in the same manneras those coated with the spray dried satin white. The results of thesetests are summarized in the following table.

In this example a sample of the satin white prepared according toExample 1 is diluted with water to a solids content of 5% by wt. Thedispersant Calgon is then admixed with the slurry in a quantity equal to1% by wt. of the solid satin white content of the slurry. The slurry isthen dried in an oven at a temperature of 50 C. until the product isdried. When tested for its ability to disperse in water the driedmaterial is observed to form agglomerates rather than the desireddispersion.

Example 6 In this example the same procedure of spray drying is followedas in Example 3 with the exception that the material is spray driedusing an inlet air temperature of 800 F. and an outlet air temperatureof 400 F. The resulting product is found not to be satisfactorilydispersible in water, but instead forms agglomerates.

From t he aboveexamplesTt can be seen that the coating properties of thesatin white dried according to our invention is virtually equivalent tothat of the initial undn'ed paste. Also where the satin white is ovendried or spray dried without following the temperature controlconditions of our invention, the resulting product is not satisfactorilydispersible in water.

Obviously many modifications and variations of the invention, describedhereinabove and in the appended claims. can be made without departingfrom the essence and scope thereof.

We claim:

1. A method of drying satin white. to form a dried product which iseasily redispersible in water, which comprises the steps of:

(a) preparing a slurry of satin white having a solids content ofaboutfrom 5 to l 1% by wt..

(b) admixing a sufficient quantity of a dispersant selected from thegroup consisting of sodium hexametaphosphate, sodium polyacrylate.trisodium nitrilotriacetate and mixtures thereof, with said slurry toprovide a dispersant concentration of about from .6 to 2% by wt.. basedon the weight ofthe solid satin white in said slurry.

(c) spraying said slurry using countercurrent heating gas flow and aheating gas inlet temperature of about from 650 F. to 730 F. andcontrolling the rate offlow ofsaid heating gas such that the heating gaswill have an exit temperature of about from 250 to 350 F.. whereby saidsatin white is dried to a dry powder while still retaining a substantialportion of its water of crystallization,

(d) collecting and recovering the dried redispersible satin white powderfrom said spray drier.

m 2. The process of claim 1 wherein said heating gas inlet temperatureis about 700 F. and wherein the heating gas flow rate is controlled suchthat the exit temperature of the heating gas will be about 300 F.

3. The process of claim 2 wherein said dispersant is provided in aconcentration of about from .6 to 1% by wt.. based on the wt. of thesolid satin white. and wherein said dispersant is sodiumhexametaphosphate containing at least 65% by wt. P 0 and having N320 toP 0 ratio .of about 1.1 to l.

4. The process of claim 1 wherein said slurry is supplied to the spraydrier at ambient temperatures.

5. The process of claim 1 wherein said heating gas is air.

6. The process of claim 1 wherein said slurry is an aqueous slurry.

-7. The process of claim 3 wherein said heating gas is air.

8. The dried redispersible satin white product produced by the processof claim 1.

2. The composition of claim 1 in which the HgO amounts to 2- 27% byweight and on an oxide basis.
 3. The composition of claim i furtherincluding an effective amount of arsenic oxide or antimony oxide as afining agent.
 4. The composition of claim 1 in which said Na2O amountsto 4.50% by weight and the K2O 8.0% by weight, both on an oxide basis.5. the composition of claim4 in which said SiO@AMOUNTS TO ")PERCENT BYWEIGHT AND THE PbO 0.0percent by weight, both on an oxide basis.
 6. Anoptical glass composition according to claim 1 having a spectraltransmission curve substantially falling between the curves of thedrawing.